The efficacy of conventional optical modulators, such as Mach-Zehnder modulators (MZM), depend upon the polarization orientation of the incoming optical carrier wave, which may vary randomly as it passes through the fiber media between the optical carrier light source and the modulator.
A number of previously-disclosed transmissive-type modulators have been shown to modulate an optical carrier wave independently of its polarization. For example, U.S. application Ser. No. 15/417,569 (incorporated by reference in its entirety), discloses a polarization insensitive integrated optical modulator which may be based on a four-port modulator (FPM) such as a four-port in-phase/quadrature-phase modulator (IQM) or a four-port MZM. These FPMs are sometimes called “cross-state” modulators. Similarly, U.S. application Ser. No. 15/601,706 (incorporated by reference in its entirety) discloses a transmissive-type modulator based on a four-port micro-ring (MR) resonator which modulates an optical carrier wave independently of the incoming carrier's polarization. This type of FPM is sometimes called a “bypass-state” modulator.
Polarization-insensitive transmissive-type modulators (PITMs) can be used in conjunction with wavelength-division multiplexing (WDM). In FIG. 1, which is comparable to a portion of FIG. 7 of U.S. application Ser. No. 15/417,569, WDM modulator 110 receives a multi-wavelength continuous wave (CW) light 100 and produces a multi-wavelength modulated signal 180. Light source 102 produces multi-wavelength CW light 100 and sends it to WDM modulator 110 via fiber 104. At demultiplexor 118, multi-wavelength CW light 100 is demultiplexed into individual, single-wavelength CW lights 1201-120n, each of which are then modulated by polarization-insensitive transmissive type 1241-124n, which can be based on, for example, cross-state or bypass-state four port modulators. The modulated output signals 1261-126n are then combined into a multi-wavelength modulated signal 180 by multiplexor 130.
However, the foregoing design has proven deficient in terms of size, cost, and complexity.